The present invention relates to a shift-assisting device for reducing the shifting operation force in changing the speed of a transmission mounted on a vehicle.
Large trucks and buses that require a large shifting force for changing the speed have been equipped with a shift-assisting device for executing the shifting operation with a decreased force. The shift-assisting device with which large vehicles are furnished generally uses compressed air as a source of operation. The shift-assisting device that uses compressed air as the source of operation is equipped with a shift actuator comprising a pneumatic pressure cylinder that operates the speed-change operation mechanism coupled to a speed-change lever in the same direction as the direction in which the speed-change lever is shifted. Large vehicles generally use compressed air as a source for operating the brake and are, hence, able to use the compressed air for the shift-assisting device. However, small- and medium-sized vehicles that are not equipped with a compressor as a source of compressed air, cannot be provided with a shift-assisting device that uses a shift actuator which comprises a pneumatic pressure cylinder. In recent years, however, it has been desired to provide even small- and medium-sized vehicles with the shift-assisting device, and there have been proposed shift-assisting devices using an electric motor, as taught in, for example, Japanese Laid-open Patent Publication (Kokai) No. 87237/1993 (JP-A 5-87237) and Japanese Patent No. 2987121. In a shift-assisting device using an electric motor, it is desired that the driving force of the electric motor be controlled depending upon the manner of operating the speed-change lever by the driver so that a smooth shifting operation can be conducted. According to the shift-assisting devices disclosed in the above Japanese Laid-open Patent Publication (Kokai) No. 87237/1993 and Japanese Patent No. 2987121, the force for operation of the speed-change lever toward the direction of shift is detected, and the driving force of the electric motor is controlled according to this force of operation. Further, Japanese Patent No. 2987121 discloses a technology in which the speed of the shifting operation is detected and the rate of the driving force of the electric motor is increased with an increase in the speed of the shifting operation.
In shifting a transmission equipped with a synchronizing mechanism, the largest operation force is required for bringing the gears into engagement in a synchronizing operation in the gear-engaging operation, and then, a second largest force is required for engaging the chamfer of dog teeth with the chamfer of the spline of the clutch sleeve. And, in an gear-disengaging operation, an operation force is required during from the start of the gear-disengaging operation until the dog teeth are disengaged from the spline of the clutch sleeve. In a shift-assisting device for controlling the driving force of an electric motor according to the operation force, however, the electric motor is driven after the operation force has reached a predetermined value, and, hence, there exists a time lag until the assisting force is produced after the operation force has increased. In shifting the transmission, therefore, the driver feels a large force just before the assisting force is produced by the electric motor. In order to solve this problem, the present applicant has proposed in Japanese Patent Application No. 46173/2000 a shift-assisting device for a transmission, equipped with a shift stroke sensor that detects the shift stroke position of the shifting mechanism and controls an electric motor for assisting the shifting operation correspondingly to the shift stroke position based on a detection signal from the shift stroke sensor.
Drivers have their peculiar habits of conducting the speed-change operation and, hence, it is also desired to control the shift-assisting force by taking into consideration the habits of the drivers. As for habits of the drivers for conducting the speed-change operation, the shifting operation speed may appear as the greatest element in determining the shift-assisting force. Namely, it is desired to increase the shift-assisting force with an increase in the shifting operation speed. However, the shifting operation speed greatly varies depending upon the shift stroke position of the shifting mechanism. That is, the shifting operation speed varies depending upon the gear-disengaging operation and the gear-engaging operation. Further, even in the gear-engaging operation, the operation speed in the synchronizing operation greatly differs from that in other shift stroke regions. It is therefore desired to detect the operation speed in a shift stroke region reflecting the peculiar habit of the driver and to determine the shift-assisting force based on t his operation speed.
It is an object of the present invention to provide a shift-assisting device for a transmission, which determine s the shift-assisting force based on an average value of the speeds of operation in a predetermined shift strok e section where the habit of a driver is greatly reflected.
In order to accomplish the above-mentioned object, the present invention provides a shift-assisting device for a transmission, equipped with an electric motor for operating a shifting mechanism in the same direction as the direction in which a speed-change lever is shifted, the shifting mechanism being coupled to the speed-change lever and actuating a synchronizing mechanism of the transmission, the shift-assisting device for a transmission comprising:
a shift stroke sensor for detecting a shift stroke position of the shifting mechanism;
a shifting direction detection means that produces signals corresponding to the operation of the speed-change lever in a first shifting direction and in a second shifting direction; and
a controller for producing a drive signal to the electric motor based on signals detected by the shift stroke sensor and by the shifting direction detection means;
wherein the controller judges whether the gear is to be disengaged or engaged based on the shifting direction of the speed-change lever and on the shift stroke position of the shifting mechanism, detects the shifting operation speed and obtains an average shifting operation speed in the gear-disengaging operation or in the gear-engaging operation, determines the electric power for driving the electric motor based on the average shifting operation speed, and drives the electric motor with a drive electric power that has been determined.
It is desired that the shifting operation speed in the gear-disengaging operation be an operation speed in a predetermined section from a shift stroke position where the clutch sleeve of the synchronizing mechanism is disengaged from the dog teeth to a neutral position. It is further desired that the shifting operation speed in the gear-engaging operation be an operation speed in a predetermined section from a position where the synchronization of the synchronizing mechanism ends to a final shift stroke position.
The electric power for driving the electric motor is obtained by adding up an initial set-point electric power that is set correspondingly to the shift stroke position and a corrected electric power calculated based on the average shifting operation speed in the gear-disengaging operation.